#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>

int main(int argc, char *argv[]) {
    int i, b = 1;
    int n;
    scanf("%d", &n);//3
    double sum = 0;
    for (i = 0; i < n; i++) {//0 1 2 3
        sum = sum + 1.0 / b;//1 + （1+1/3）+ (1+1/3+1/5) 
        b = b + 2;//3 5 7
    }  
    printf("%.2f", sum * 1.0);//.2是精确到小数点后两位的意思
    return 0;
}